I recently shot a wedding together with a good friend for mutual friends and we later displayed our JPGs on a very good TV screen for the wedding party. My D600 images loaded very quickly, almost instantly and the slide show was smooth... my friend's D800 loaded, bit, by bit, by bit by .... it was taking over 5 seconds, drip by drip to load each picture! Smooth... actually painful for the audience and it was aborted. When the images did load, we used identical 24-70 F2.8 ED lenses + SB910 flashguns, we could see no discernible quality difference on the screen!

This is pointless. Either of these cameras can produce jpgs in sizes ranging from small to large. Your friend needs to learn how to operate his camera. This has nothing to do with the pros and cons of one camera over the other.